This application is based upon and claims the benefit of priority of Japanese Patent Applications No. 2001-351182 filed on Nov. 16, 2001 and No. 2002-149318 filed on May 23, 2002, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a fuel injection nozzle in which a needle slidably fitted to a guide hole of a nozzle body stepwise lifts for injecting fuel.
2. Description of the Prior Art
Conventionally, as disclosed in JP-U-63-51154, JP-A-5-321789 and so on, a fuel injection nozzle is known, in which stepwise lift of a needle causes injection bores arranged axially up and down to sequentially open for injecting fuel. A first conventional fuel injection nozzle disclosed in JP-U-63-51154 has first injection bores opened to a seat surface of a nozzle body and second injection bores opened to a sack chamber of the nozzle body. A seat contact of a needle controls to open and close the first injection bores and a shaft tip of the needle inserted into the sack chamber controls to open and close the second injection bores.
A second conventional fuel injection nozzle disclosed in JP-A-5-321789 has fist and second injection bores provided axially at given intervals in a sack chamber of a nozzle body and a shaft tip of the needle inserted in the sack chamber controls to open and close both of the first and second injection bores.
However, the first conventional injection nozzle has a drawback that it is very difficult and costly to precisely form the sack chamber to secure better sliding inner surface of the sack chamber that comes in contact with the shaft tip of the needle without fuel leakage, since the sack chamber is positioned at the deepest bottom of the nozzle body and sack diameter thereof is relatively small.
Further, when fuel is supplied to the second injection bores after the first injection bores have been opened, fuel flows at high speed along the sliding inner surface of the sack chamber so that the sliding inner surface tends to be worn out by foreign material contained in the fuel. Furthermore, as the sack chamber provided at a leading end of the nozzle body is exposed to high temperature combustion gas, hardness of the shaft tip of the needle is likely reduced so that the shaft tip is prone to wear. As a result, when the needle is at a position where the second injection bores are closed and only first injection bores are opened, fuel is likely to be injected into an engine combustion chamber from the second injection bores due to the fuel leakage along the sliding inner surface of the sack chamber that has been worn out, which results in increasing black smoke and hydrocarbon contained in exhausted combustion gas.
In the second conventional fuel injection nozzle, the sack diameter is relatively large since the first injection bores are positioned in the sack chamber and it is required to secure sufficient fuel flow passage area therein. Consequently, it is inevitable that seat diameter is relatively large and pressure receiving area of the needle on which fuel pressure acts tends to be relatively small, failing in securing sufficient valve opening force so that response characteristic of opening and closing the injection bores is poorer.
Further, it is very difficult and costly to precisely form the sliding inner surface of the sack chamber, similarly to the first conventional fuel injection nozzle.
An object of the present invention is to provide a fuel injection nozzle for injecting high pressure fuel in which a nozzle body member is easily manufactured to limit inadequate fuel leakage so that emissions such as black smoke and hydrocarbon are reduced.
To achieve the above object, in the fuel injection device, a nozzle body member is provided inside with a guide hole having a conical inner circumferential wall in a vicinity of an end thereof and a cylindrical inner circumferential wall axially above the conical inner circumferential wall, with at least a first injection bore whose one end is opened to the conical inner circumferential wall and whose another end is opened to outside, and on an axially above side of the first injection bore with at least a second injection bore whose one end is opened to one of the conical and cylindrical circumferential walls and whose another end is opened to outside. A needle member is inserted into the guide hole and the needle member is provided in a vicinity of an end thereof with a circular seat contact coming in contact with the conical inner circumferential wall, on an axially above side of the seat contact with a guide shaft whose outer diameter is larger than that of the circular seat contact and which is slidably fitted to the cylindrical circumferential wall, and with a fuel passage extending inside the guide shaft for introducing fuel to the first and second injection bores.
With the fuel injection nozzle mentioned above, when the needle member does not lift, the circular seat contact is in contact with the conical inner circumferential wall and the fuel passage does not communicate with both the first and second injection bores, when the needle member shows a first lift, the circular seat contact moves in a direction of leaving the conical inner circumferential wall and the fuel passage communicates with the first injection bore through a clearance between the circular seat contact and the conical inner circumferential wall but the guide shaft interrupts communication between the fuel passage and the second injection bore, and, when the needle member shows a second lift, the circular seat contact further moves in a direction of leaving the conical inner circumferential wall and, in addition to the communication between the fuel passage and the first injection bore, the guide shaft allows the communication between the fuel passage and second injection bore.
According to the fuel injection nozzle mentioned above, as the cylindrical inner circumferential wall is formed axially above the position where the sack chamber of the conventional fuel injection nozzle is provided and inner diameter of the cylindrical inner circumferential wall is larger than that of the sack chamber, the cylindrical inner circumferential wall is more easily formed at lower cost, compared with the conventional fuel injection nozzle in which the tip of the guide shaft is inserted into the sack chamber.
It is preferable that the needle member is provided axially above the guide shaft with an upper small diameter portion and axially below the guide shaft with a lower small diameter portion and the fuel passage is a plurality of through-holes each axially penetrating from an upper end of the guide shaft radially outside the upper small diameter portion to a lower end thereof radially outside the lower small diameter portion and axially above the circular seat contact. Further, the one end of the first injection bore is arranged axially below a position where the circular seat contact comes in contact with the conical inner circumferential wall, and outer circumference of the guide shaft serves, when the needle member does not lift or shows the first lift, to close the one end of the second injection bore and, when the needle member shows the second lift, to open the one end of the second injection bore.
Preferably, the guide shaft is provided at the lower end thereof radially outside the lower small diameter portion with a guide shaft ring groove to which the through-holes are opened so that the lower end circumference of the guide shaft radially outside the guide shaft ring groove constitutes a thin thickness wall. Accordingly, when the needle member does not lift or shows the first lift and the guide shaft ring groove is filled with high pressure fuel, the thin thickness wall of the lower end of the guide shaft expands radially outward so that the guide shaft fluid-tightly closes the one end of the second injection bore and suppresses fuel leakage from the second injection bore.
As an alternative, the fuel passage may has a lateral hole radially extending in the guide shaft at a position axially above an upper end of the cylindrical inner circumferential wall and a vertical hole whose one end is opened to the lateral hole, which axially extends through a center of the guide shaft and whose another end is opened to a lower end of the needle member axially below the circular seat contact. Further, the end of the first injection bore is arranged axially above a position where the circular seat contact comes in contact with the conical inner circumferential wall, and outer circumference of the guide shaft serves, when the needle member does not lift or shows the first lift, to close the one end of the second injection bore and, when the needle member shows the second lift, to open the one end of the second injection bore.
Further, it is preferable that the nozzle body member comprises a nozzle body and a ring shaped guide member whose outer circumference is press fitted into an inner circumference of the nozzle body. The ring shaped guide member has the cylindrical inner circumferential wall from which the second injection bore extends via both insides of the ring shaped guide member and the nozzle body to outside of the nozzle body. Since the cylindrical inner circumferential wall is formed in the ring shaped guide member that is a body separated from the nozzle body, the cylindrical inner circumferential wall can be more easily and precisely manufactured.
Moreover, it is preferable that both of the nozzle body and the ring shaped guide member have positioning portions with reference to which relative circumferential position between the nozzle body and the ring shaped guide member is defined. The respective positioning portions serve to secure an accurate relative circumferential position between the nozzle body and the ring shaped guide member, when the ring shaped guide member is formed separately from and, then, is press fitted into the nozzle body.
Furthermore, as an alternative, the needle member may have an outer needle provided inside with a cylindrical through-hole and in a vicinity of an end thereof with another circular seat contact coming in contact with the conical inner circumferential wall, and an inner needle slidably fitted to the cylindrical through-hole. The outer needle constitutes the guide shaft and the inner needle has the circular seat contact and the fuel passage. With this construction, when the needle member does not lift, both the circular and another circular seat contacts are in contact with the conical inner circumferential wall, when the needle member shows the first lift, only the inner needle moves and the outer needle does not move, and, when the needle member shows the second lift, the outer needle moves together with the inner needle.
Preferably, the fuel passage has a lateral hole radially extending in the inner needle at a position axially above an upper end of the outer needle and a vertical hole whose one end is opened to the lateral hole, which axially extends through a center of the inner needle and whose another end is opened to a lower end of the inner needle axially below the circular seat contact. Further, the one end of the first injection bore is arranged axially above a position where the circular seat contact comes in contact with the conical inner circumferential wall and axially below a position where the another circular seat contact comes in contact with the conical inner circumferential wall, the one end of the second injection bore is arranged at the conical inner circumferential wall axially above the position where the another circular seat contact comes in contact with the conical inner circumferential wall, and, when the needle member shows the first lift, the fuel passage communicates only with the first injection bore through the clearance between the circular seat contact and the conical inner circumferential wall and, when the needle member shows the second lift, the fuel passage communicates with the second injection bore through a clearance between the another circular seat contact and the conical inner circumferential wall.
Preferably, the inner and outer needles are provided with lift force transmitting means through which a lift force is transmitted from the inner needle to the outer needle at least when the needle member shows the second lift.
Further, it is preferable that at least one of the outer circumference of the guide shaft and the cylindrical inner circumferential wall is provided axially above the second injection bore with a ring shaped collection groove and the nozzle body member is provided with a collection passage whose one end communicates with the collection groove and whose another end communicates with a low pressure source, whereby the high pressure fuel entering a clearance between the outer circumference of the guide shaft and the cylindrical inner circumferential wall is returned through the collection groove and the collection passage to the low pressure source.
The collection groove serves not only to promote fuel lubrication in the clearance between the outer circumference of the guide shaft and the cylindrical inner circumferential wall is promoted but also to suppress fuel leakage through the second injection bore when the needle member does not lift or shows the first lift.
In case of the fuel injection nozzle having the inner and outer needles mentioned above, it is preferable that the outer needle is further provided with a radial through-hole whose one end communicates with the ring shaped collection groove when the needle member does not lift and the inner needle is provided on outer circumference thereof with a ring groove coming in communication with another end of the radial through-hole when the needle member shows the first lift. With the construction mentioned above, the high pressure fuel entering a clearance between the outer circumference of the outer needle and the cylindrical inner circumferential wall is returned through the collection groove and the collection passage to the low pressure source and the high pressure fuel entering a clearance between an outer circumference of the inner needle and an inner circumference of the outer needle is returned through the ring groove, the radial through-hole, the collection groove and the collection passage to the low pressure source.
Since the inner needle has the ring groove, high pressure fuel entering the clearance between the inner and outer needles is stored in the ring groove when the needle member does not lift so that not only fuel lubrication in the clearance between the inner and outer needles is promoted, but also fuel leakage through the first injection bore is suppressed.